1. Field of the Invention
This invention relates to a method of making moulds, and mould cores from refractory sand. The moulds or mould-parts may be used in a foundry to make castings of ferrous or non-ferrous metal. The invention also relates to a method of cooling sand.
2. Description of the Prior Art
There are two main types of refractory composition from which parts of moulds are made. One type, generally referred to as green sand, employs refractory sand, starch, water and a carbonaceous material such as coal dust. The other type of composition is characterised in that in addition to refractory sand, a resin binder is employed. The resin is generally of the thermosetting type. With such compositions including a resin binder, the necessary ingredients are fed into a mixer and mould parts are then formed from the resulting mixture. The process of forming the parts of the mould requires the binder to be cured. Generally, a catalyst is mixed with the sand and the binder to accelerate curing.
The problem arises, particularly in hot weather, that the curing process can start in the mixer with the consequence that by the time the mixture enters the moulding station it is no longer free-flowing and is thus unusable so far as the making of mould parts is concerned.
Although a hot environment in the foundry is typically a cause of the sand mixture entering the moulding station at too high a temperature, sometimes the sand itself may be supplied to the foundry at too high a temperature.
It is important to avoid premature setting of the resin. To this end foundries commonly specify that the sand must be supplied at below a chosen maximum temperature, typically in the order of 26.degree. C.
The sand is obtained by quarrying. Since the sand so obtained is wet it is necessary to heat the sand so as to dry it. Typically, this is done by fluidising the sand with hot air. This raises the temperature of the sand. It is thus necessary to cool it. This is conventionally done by means of a fluidised bed cooling technique. The warm sand is fed into a chamber and fluidised by ambient air. This enables intimate contact to take place between each grain of sand and the air. Sometimes the cooling effect of the air is supplemented by passing water through heat exchange tubes within the bed. Since the air is at ambient temperature, the sand will effectively be cooled to below the chosen temperature in all but hot summer weather unless a longer period of heating than usual is required to dry the sand, thereby increasing the temperature of the sand to above that at which it normally enters the fluidised bed. Once the sand has been cooled it is passed into a large storage hopper. From time to time regular deliveries of the sand from the storage hopper are made to foundries in a suitable vehicle. The thermal insulation properties of sand are such that a hot batch of sand (ie. a batch of sand above the chosen temperature) will remain at that temperature for long periods. Thus, when such a batch of sand reaches the bottom of the hopper it will still be at an undesirably high temperature and will be delivered at that temperature to the foundry.